It is common for locking systems to provide separate operating keys and control keys for use with rotatable locking cores. An operating key is employed to lock and unlock a corresponding core when the core is housed in the locking mechanism. For example, if a locking mechanism is installed to secure a desk drawer against opening when locked, the operating key may be used to lock and unlock the core, thereby in turn, permitting the secure closure and opening, respectively, of the drawer.
A control key may be used for additional functions including, acting as a master key to operate a number of different locking cores or as a key to permit removal of a locking core from its corresponding housing. Typically, a control key is provided with a bitted portion which is capable of activating one or more control tumblers in a locking core. When such control tumblers are activated, usually upon insertion and rotation of the control key to a predetermined position, removal of the locking core from the housing may be achieved. Alternately, where a control key functions as a master key, the bitted portion of the control key is adapted to activate the tumblers in a number of different locking cores which use separate operating keys.
In locking systems of the prior art, the manufacture and use of separate operating keys and master keys gave rise to inherent disadvantages.
Moreover, the prior art includes a number of two part keys for use as security keys. The underlying theory is that one person should keep one part of the key and another person should keep another part of the key and that only when the parts are combined is the lock operable. Such a two part key is disclosed by Glidden in U.S. Pat. No. 1,979,798. Such keys, in their shaft portion where torque is appreciable on turning the key, may be subject to separation of the shaft parts due to different torques on different parts of the shaft. To provide a combination key when the broken shaft is splinted to minimize breaking apart of the parts on application of torque may have been thought impracticable due to the width of most keyways. In any event two part keys having lateral shaft support are not presently known to the applicant.